1. Field of the Invention
The present invention relates generally to a hue control circuit and is directed more particularly to an improved hue control circuit for use with a hue corrector of a video signal processor.
2. Description of the Prior Art
A prior art hue control circuit is constructed as shown in FIG. 1. That is, a constant frequency signal (constant wave) CW generated by an oscillator 1A is phaseshifted by 90 degrees in a 90.degree. phase shifter 2A and then balance-modulated in a balanced modulator 3A by a color difference signal, for example, (B-Y) color difference signal fed thereto through an input terminal 10A. The output signal CW from the oscillator 1A is also fed to a balanced modulator 4A and then balance-modulated by a color difference signal (R-Y) fed thereto through an input terminal 11A. The respective carrier chrominance signals thus provided are supplied to a mixer 7A and then mixed with each other.
The output signal from the oscillator 1A is further fed to a modulator 5A and therein modulated by a burst flag signal supplied thereto from an input terminal 12A. The modulated signal therefrom is supplied to a variable phase shifter 6A and thereby phase-shifted to have a predetermined phase. The phase shifting amount of this variable phase shifter 6A can be controlled by a control device 8A. The output from the variable phase shifter 6A is called as a color burst signal and serves as a reference signal for determining the hue. This color burst signal is supplied to the mixer 7A and mixed to the above-mentioned carrier chrominance signals to provide a normal carrier chrominance signal which is then delivered to an output terminal 9A.
According to the prior art hue control circuit described as above, a variable resistor Vr of the control device 8A is varied to shift the phase of the color burst signal and to thereby correct the hue. This prior art hue control circuit, however, can not be free from the following defects. That is, the color burst signal is provided separately so that there are required the modulator therefor and the phase shifter to vary the phase thereof. Further, due to the thermal characteristics, scattering and so on of the variable phase shifter 6A and the control device 8A, the phase of the burst signal which is once preset accurately is varied.